Exhaust plenum chamber constructions including thermal barrier coatings for opposed-piston engines

ABSTRACT

An exhaust plenum chamber with a thermal barrier coating for an opposed-piston engine reduces heat rejection to coolant, while increasing exhaust temperatures, fuel efficiency, and quicker exhaust after-treatment light-off. The exhaust plenum chamber can include a coating on the inside surface of the chamber. Posts which are structural and provide cooling channels or passageways can be present in the exhaust plenum chamber and coated with the thermal barrier coating material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application number PCT/US2018/045650, titled “Exhaust Plenum Chamber Constructions Including Thermal Barrier Coatings for Opposed-Piston Engines,” filed Aug. 7, 2018, which claims priority to U.S. Provisional Patent Application No. 62/547,379, titled “Exhaust Plenum Chamber Constructions Including Thermal Barrier Coatings for Opposed-Piston Engines,” filed Aug. 18, 2017.

This application contains subject matter related to that of commonly-owned U.S. patent application Ser. Nos. 14/450,808, filed Aug. 4, 2014, “Exhaust Layout With Accompanying Firing Sequence For Two-Stroke Cycle, Inline, Opposed-Piston Engines” now U.S. Pat. No. 10,001,057, issued Jun. 19, 2018; Ser. No. 14/284,058, filed May 21, 2014, “Air Handling Constructions for Opposed-Piston Engines,” now U.S. Pat. No. 9,581,024, issued Feb. 28, 2017; and Ser. No. 14/284,134, filed May 21, 2014, “Open Intake and Exhaust Chamber Constructions for an Air Handling System of an Opposed-Piston Engine,” now U.S. Pat. No. 9,551,220, issued Jan. 24, 2017.

FIELD

The field concerns internal combustion engines. In particular, the field relates to opposed-piston engines which may be applied to vehicles, vessels, and stationary power sources.

BACKGROUND

A two-stroke cycle engine is an internal combustion engine that completes a cycle of operation with a single complete rotation of a crankshaft and two strokes of a piston connected to the crankshaft. The strokes are typically denoted as compression and power strokes. One example of a two-stroke cycle engine is an opposed-piston engine in which two pistons are disposed in the bore of a cylinder for reciprocating movement in opposing directions along the central axis of the cylinder. Each piston moves between a bottom dead center (BDC) location where it is nearest one end of the cylinder and a top dead center (TDC) location where it is furthest from the one end. The cylinder has ports formed in the cylinder sidewall near respective BDC piston locations. Each of the opposed pistons controls one of the ports, opening the port as it moves to its BDC location, and closing the port as it moves from BDC toward its TDC location. One of the ports serves to admit charge air into the bore, the other provides passage for the products of combustion out of the bore; these are respectively termed “intake” and “exhaust” ports (in some descriptions, intake ports are referred to as “air” ports or “scavenge” ports). In a uniflow-scavenged opposed-piston engine, pressurized charge air enters a cylinder through its intake port as exhaust gas flows out of its exhaust port, thus gas flows through the cylinder in a single direction (“uniflow”) along the length of the cylinder, from intake port to exhaust port.

Charge air and exhaust products flow through the cylinder via an air handling system (also called a “gas exchange” system). Fuel is delivered by injection from a fuel delivery system. As the engine cycles, a control mechanization governs combustion by operating the air handling and fuel delivery systems in response to engine operating conditions. The air handling system may be equipped with an exhaust gas recirculation (“EGR”) system to reduce production of undesirable compounds during combustion.

In an opposed-piston engine, the air handling system moves fresh air into and transports combustion gases (exhaust) out of the engine, which requires pumping work. The pumping work may be done by a gas-turbine driven pump, such as a compressor (e.g., a turbocharger), and/or by a mechanically-driven pump, such as a supercharger. In some instances, the compressor unit of a turbocharger may be located upstream or downstream of a supercharger in a two-stage pumping configuration. The pumping arrangement (single stage, two-stage, or otherwise) can drive the scavenging process, which is critical to ensuring effective combustion, increasing the engine's indicated thermal efficiency, and extending the lives of engine components such as pistons, rings, and cylinders. Additionally, pressure and suction waves in the intake and exhaust can also provide pumping work. The pumping work also drives an exhaust gas recirculation system.

Opposed-piston engines have included various constructions designed to transport engine gasses (charge air, exhaust) into and out of the cylinders. For example, U.S. Pat. No. 1,517,634 describes an early opposed-piston aircraft engine that made use of a multi-pipe exhaust manifold having a pipe in communication with the exhaust area of each cylinder that merged with the pipes of the other cylinders into one exhaust pipe. The manifold was mounted to one side of the engine.

In the 1930's, the Jumo 205 family of opposed-piston aircraft engines defined a basic air handling architecture for dual-crankshaft opposed-piston engines. The Jumo engine included an inline cylinder block with six cylinders. The construction of the cylinder block included individual compartments for exhaust and intake ports. Manifolds and conduits constructed to serve the individualized ports were attached to or formed on the cylinder block. Thus, the engine was equipped with multi-pipe exhaust manifolds that bolted to opposite sides of the engine so as to place a respective pair of opposing pipes in communication with the annular exhaust area of each cylinder. The output pipe of each exhaust manifold was connected to a respective one of two entries to a turbine. The engine was also equipped with intake conduits located on opposing sides of the engine that channeled charge air to the individual intake areas of the cylinders. A two-stage pressure charging system provided pressurized charge air for the intake conduits.

The prior art exhaust manifolds extracted a penalty in increased engine size and weight. Each individual pipe required structural support in order to closely couple the pipe opening with the annular exhaust space of a cylinder. Typically, the support was in the form of a flange at the end of each pipe with an area sufficient to receive threaded fasteners for fastening the flange to a corresponding area on a side of the cylinder block. The flanges of each manifold were arranged row-wise in order to match the inline arrangement of the cylinders. The width of the ducts connected to these flanges restricted cylinder-to-cylinder spacing, which required the engine to be comparatively heavy and large.

In modern vehicle engines, size, weight and performance, both in terms of power and emissions, are factors that are balanced in designing engine components. It is desirable to minimize the engine space that receives exhaust from the cylinders after each combustion event so as to reduce size and weight and improve performance. In modern designs of uniflow-scavenged, opposed-piston engines these objectives are approached by elimination of external manifolds to transport engine gases. These engines can include an open exhaust plenum chamber (also called an exhaust chest) where all of the cylinder exhaust ports are situated. All exhaust discharged from all of the cylinders is collected in the interior space of the exhaust plenum chamber and then is transported out of the cylinder block to downstream components of an exhaust system.

It is desirable to retain as much heat as possible in the exhaust gas discharged into the exhaust plenum chamber in order to maximize the thermal energy extracted downstream for useful purposes such as driving a turbine and energizing after treatment devices (e.g., providing heat for catalysis). However, heat can be lost by conduction through the structures and surfaces of the exhaust plenum chamber, as well as exhaust system structures downstream. Once received in the surrounding structure, heat is conducted from the cylinder block by an engine cooling system in order to limit thermal stress on the cylinder block. Thermal energy lost in this way is said to be “rejected” to the coolant. Circulation of the coolant adds to parasitic engine losses. Therefore, it is desirable to reduce the transfer of heat from the exhaust gas to structures and surfaces of the exhaust plenum chamber which surround the space into which the exhaust gas is expelled from the exhaust ports so as to enhance the thermal efficiency of the engine.

SUMMARY

In some implementations an opposed-piston engine is provided with an open exhaust plenum chamber construction that has one or more thermal barrier coatings. The exhaust plenum chamber can include an inside surface and the thermal barrier coating can be on the inside surface.

In some aspects, an opposed-piston engine has a plurality of cylinders formed or supported in a cylinder block with an exhaust chest that receives exhaust from all of the cylinders of the engine. The exhaust chest comprises a thermal barrier coating, or layer, applied to at least one inside surface of the exhaust plenum chamber in order to reduce the transfer of heat from the exhaust gas to the cylinder block.

The following features can be present in the exhaust plenum chamber and/or in the engine in any suitable combination. The exhaust plenum chamber can include at least one post (e.g., a structural, outrigger post) for transferring force between opposing walls of the exhaust plenum chamber. In some implementations, the at least one post can include a substantially axial conduit or passageway in fluid communication with a cooling system of the engine. The thermal barrier coating can include a thermally insulating material, and in some implementations, the thermally insulating material can have a low coefficient of thermal conductivity. The coating can include any of zirconia, alumina, a chrome-containing composition, a cobalt-containing composition, a nickel-containing composition, an yttrium-containing composition, and any combination thereof. The coating can be spray deposited or dip coating deposited onto the inside surface of the exhaust chest (i.e., exhaust plenum chamber). In some implementations, the exhaust plenum chamber can include a metallic surface comprising a base material, and the base material can include gray iron.

In a related aspect, a method of making an exhaust plenum chamber for a uniflow-scavenged, opposed-piston engine includes applying a coating of a material of low thermal conductivity to an inside surface of the exhaust plenum chamber. The exhaust plenum chamber can include at least one post for transferring a compressive force between opposing walls of the exhaust plenum chamber. The following features can be present in the method in any suitable combination. The method can include preparing interior surface of the exhaust plenum for application of the coating. Additionally, or alternatively, the method can include treating the exhaust plenum chamber after application of the coating. The exhaust plenum chamber can also include a floor and a ceiling, and the at least one post can extend from the floor to the ceiling.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures, FIG. 1 is a schematic diagram of an opposed-piston engine and an air handling system for use with the engine, and is properly labeled “Prior Art.”

FIGS. 2A and 2B show an exemplary opposed-piston engine, and are properly labeled “Prior Art.”

FIGS. 3A and 3B show an exemplary cylinder assembly for use with the opposed-piston engine of FIG. 1, and are properly labeled “Prior Art.”

FIGS. 4A and 4B show an exemplary exhaust plenum chamber according to this disclosure including a cylinder assembly shown in FIGS. 3A and 3B.

FIG. 4C is a schematic showing a cooling system fluidly coupled to a support post in the exhaust plenum chamber of FIGS. 4A and 4B.

FIG. 5 is a schematic diagram showing an exhaust channel fluidly coupled to the exhaust plenum chamber of FIGS. 4A and 4B.

FIG. 6 shows a close-up cross-sectional view of a coating on an inside surface of the exhaust plenum chamber of FIGS. 4A and 4B.

FIG. 7 shows an exemplary method for making an exhaust plenum chamber according to this specification.

FIG. 8 is a plot showing the percent change in heat relative to an exhaust plenum chamber without a coating.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An opposed-piston engine with a cylinder block having an exhaust plenum chamber and a thermal barrier coating on an inside surface of the exhaust plenum chamber is described. The thermal barrier coating, or coating layer, can serve to provide higher exhaust temperatures, reduce heat rejection to coolant in the engine, and allow for higher fatigue strength in the exhaust plenum chamber and its structural features. Higher exhaust temperatures can improve an engine's fuel efficiency by increasing the exhaust enthalpy driving the engine's turbocharger. Additionally, or conversely, the higher exhaust temperatures can allow an engine's after-treatment system to light-off more quickly and maintain an operating temperature when the engine is operating at lower speeds or under lower loads. Also described herein are details of the coating, including methods for application of coating materials.

FIG. 1 is a schematic diagram 100 showing a general example of an opposed-piston engine 110 and an air handling system of the engine, according to the prior art. The opposed-piston engine 110 is shown as having a plurality of cylinders 111, an intake plenum chamber 120, and an exhaust plenum chamber 115. The air handling system is in fluid communication with an intake plenum chamber 120 and an exhaust plenum chamber 115 and includes an air inlet 101, an air filter 145, a turbo-charger 121 with a compressor 140 and a turbine 125, a charge air cooler 150, an exhaust gas recirculation (EGR) mixer 175, a supercharger 160, an intercooler 165, a recirculation valve 170, an EGR valve 130, an EGR cooler 155, a back pressure valve 177, an after-treatment system 135, and an exhaust outlet 199. The after-treatment system 135 can include one or more after-treatment devices (e.g., an after-treatment system, one or more particulate filters, etc.), which may include a temperature dependent component that operates best at temperatures over about 150° C.

FIGS. 2A and 2B show a representative opposed-piston engine 200 in assembled form including a cylinder block 202. This specific engine example corresponds to the engine described in related U.S. Pat. No. 9,581,024. The cylinder block 202 is a single monolithic element with an integrated structure that includes cylinders, coolant and lubricating passages, crankcases, an open intake plenum chamber, and an open exhaust plenum chamber. The cylinder block 202 is manufactured by known methods of engine block fabrication such as casting, machining, and/or printing. The engine is configured to be compact so as to occupy minimal space in applications such as vehicles, locomotives, maritime vessels, stationary power sources, and so on. Air handling components of the engine 200 include a turbocharger 210, a supercharger 214, an intake plenum chamber 240, an exhaust plenum chamber 245, and various pipes, manifolds, and conduits. With the exception of the intake and exhaust plenum chambers, these elements may be supported on the cylinder block using conventional means. The intake and exhaust plenum chambers are formed as elongate, open galleries or chests inside the cylinder block when the block is being manufactured.

The turbocharger 210 comprises an exhaust-driven turbine 211 and a compressor 213. Preferably, but not necessarily, the supercharger 214 is mechanically driven, for example by a crankshaft. The output of the compressor 213 is in fluid communication with the intake of the supercharger 214 via the conduit 217. In some aspects, a charge air cooler 215 may be placed in the airflow path between the compressor 213 and the supercharger 214. The output of the supercharger 214 is in fluid communication with the intake plenum chamber via a manifold, each branch 221 of which is coupled to a respective elongate opening of the intake chamber by way of a cover. The inlet of the turbine 211 is in fluid communication with the exhaust plenum chamber via a conduit 231 coupled to a respective elongate opening of the exhaust plenum chamber by way of a cover 230. Although not shown in these figures, the engine 200 may be equipped with a valve-controlled conduit between the exhaust plenum chamber and the supercharger 214 for EGR (exhaust gas recirculation).

FIG. 2B shows an elevation view of one side of the engine 200, with components such as the cover 230 and intake air conduit 217 removed to allow the intake plenum chamber 240 and the exhaust plenum chamber 245 to be seen. The intake plenum chamber 240 and the exhaust plenum chamber 245 open through the visible side of the cylinder block 202 and continue through to the opposite side of the cylinder block where additional openings may be provided. The cylinder block 202 is constructed with a plurality of cylinders; as a specific example, three cylinders 250 are shown in FIG. 2B, although this is not meant to be limiting. In some aspects, the cylinder block 202 may be manufactured so as to dispose the cylinders in an inline array aligned with a longitudinal direction L of the cylinder block.

FIGS. 3A and 3B show a specific example of a cylinder construction that may be provided in the cylinder block 202. Although the cylinder is shown as a liner (or sleeve) which would be retained in a tunnel in the cylinder block 202, this representation is not meant to be limiting. In fact, the cylinder can also comprise a boring or a tube formed in the cylinder block during manufacture of the block. In this specific example, the cylinder 250 (in FIG. 2B) comprises a substantially tubular liner 300 defining a sidewall 320 and a bore 337 with an interior surface. Exhaust and intake ports 326 and 325 respectively are formed in the cylinder through the sidewall, inboard of respective open ends of the cylinder. The exhaust and intake ports 326 and 325 are separated along an axial direction of the cylinder 250. The exhaust port 326 comprises at least one substantially circumferential array or series of openings through the sidewall 320. The intake port 325 comprises at least one substantially circumferential array or series of openings through the sidewall 320. Each of the open ends is characterized by the gas transport activity that occurs in the nearest port. In this regard, the end closest to the exhaust port 326 is referred to as “the exhaust end” of the cylinder. Similarly, the end closest the intake port 325 is referred to as “the intake end” of the cylinder. Injector apertures 346 are formed in a portion of the sidewall of the cylinder between the ports 325 and 326. Two pistons 335 and 336 are disposed in opposition within the bore 337. The pistons 335 and 336 have end surfaces 335 e and 336 e respectively that partially define a combustion chamber 341 when the pistons are at or near their respective top dead center (TDC) positions. The combustion chamber 341 is also partially defined by the cylinder bore 337 in the intermediate portion of the cylinder, between the intake ports 325 and the exhaust ports 326. Fuel injection components 345 are supported in the apertures 346. This specific cylinder assembly example is described in detail in related U.S. patent application Ser. No. 14/675,340, published as U.S. Publication 2016/0290277, now U.S. Pat. No. 9,845,764, issued Dec. 19, 2017.

As seen in FIG. 2B, the cylinders 250 are mutually oriented such that all of the intake ports 254 are contained in the intake plenum chamber 240 of the cylinder block 202, and all of the exhaust ports 256 are contained in the exhaust plenum chamber 245 of the cylinder block 202. The exhaust plenum chamber 245 is a single volume into which the exhaust ports of all the cylinders communicate, as opposed to an exhaust manifold. All of the exhaust gas produced by combustion which is not retained in the cylinders flows directly into the exhaust plenum chamber and from there to the downstream elements of an exhaust channel such as a turbine and one or more after-treatment devices. Similarly, the intake plenum chamber 240 contains all of the intake ports, which is to say that each and every one of the intake ports of the engine receives charge air only from the intake plenum chamber. Some advantages to such a configuration are reduced weight and more compact configuration of the engine.

FIG. 4A shows, in elevation, a portion of a cylinder block 400 of an opposed-piston engine like the engine 200 looking into an exhaust plenum chamber 405 in the cylinder block. The engine is constructed with three cylinder liners 320. The view is through a side opening of the exhaust plenum chamber 405 from which a manifold cover has been removed from the cylinder block 400 to show the exhaust port openings 326 of the cylinder liners 320. The exhaust plenum chamber 405 is defined between two opposing interior walls 409 and 410 of the cylinder block. FIG. 4B shows a cross-section of the exhaust plenum chamber 405 taken midway between the opposing interior walls 409 and 410 of the exhaust plenum chamber 405 in a plane that is orthogonal to the longitudinal axes of the cylinders 300. With the orientation of the cylinder block shown in FIG. 4A, these walls may be termed “ceiling” 409 and “floor” 410 of the exhaust plenum chamber 405, although only for the sake of this explanation. Each of the ceiling 409 and floor 410 comprises a surface; the surface of the floor 410 is seen in FIG. 4B. Support posts 415 formed integrally with the cylinder block extend between the ceiling 409 and floor 410 to provide structural support. Surfaces of the ceiling 409, the floor 410, and the support posts 415, and other elements of the exhaust plenum chamber 405 are exposed to the heat of exhaust gases flowing out of the exhaust port openings 326 during operation of the engine. In order to relieve thermal stress on the cylinder block caused by transfer of heat from the exhaust gases through those surfaces, the support posts 415 are provided with axial passageways 420 for transporting liquid coolant. The axial passageways 420 are in fluid communication with a cooling system (not shown). Such an arrangement is illustrated and described in U.S. Pat. No. 9,581,024.

FIG. 4C is a schematic that shows an enlarged view of a cross-section of a post 415 in an exhaust plenum chamber 405 that extends from the chamber ceiling 409 to the chamber floor 410, including an axial coolant passageway 420 through the post 415 and a coating 425 on the inner surface of the exhaust plenum chamber 405. The schematic in FIG. 4C also shows a cooling system 495 that is fluidly connected to the coolant passageway 420. The cooling system 495 includes a source of liquid coolant. In the engine, the coolant passageways 420 in the exhaust plenum chamber 405 connect via one or more return passageways 496R and one or more feed passageways 496F. The one or more return passageways 496R and one or more feed passageways 496F can include tunnels, conduits, or other passageways through the cylinder block, as well as any of fittings, hoses, tubing, and the like to allow coolant to flow through the passageways 420 in the posts 415 of the exhaust plenum chamber 405 and be moved about the engine.

As shown in the schematic illustration of FIG. 5, the exhaust plenum chamber 405 of FIGS. 4A, 4B, and 4C comprises an exhaust outlet 502 in fluid communication with an exhaust channel 505 through which exhaust gas can be conveyed for use by downstream components of the exhaust channel. A coating 425 on one or more inside surfaces of the exhaust plenum chamber 405 reduces heat transfer from exhaust gas to the cylinder block, thereby providing exhaust gas with a heightened enthalpy for the downstream components of the exhaust channel. In this regard, the exhaust outlet 502 places the exhaust plenum chamber 405 in fluid communication with one or more of a turbine inlet and an after-treatment device disposed in the exhaust channel 505. In this case, the sequential order of the turbine and the after-treatment device is not limiting. The exhaust plenum chamber 405 may also be in fluid communication with an EGR system 510, either by a separate exhaust outlet 512, or via a branch 514 from the exhaust channel 505.

Cylinder blocks of opposed-piston engines can be constructed of various materials. However, for ease of manufacturing, as well as because of suitable mechanical properties over a wide range of temperatures, irons and steels have been the materials of choice for making engine blocks. Though the engine blocks, and thus the exhaust plenum chambers, described herein are discussed as being of gray iron, other materials can be used, such as aluminum.

The fatigue strength of any metal used for base metal of the exhaust plenum chamber can vary as a function of temperature. For example, FIG. 10-2 of the Atlas of Fatigue Curves (Boyer, Howard E., “Atlas of Fatigue Curves,” ASM International; Materials Park, 1986, FIG. 10-2, Page 246) shows fatigue limit strength as a function of temperature for gray iron. At 600 deg. C, gray iron has fatigue limit strength of approximately 5 to 7.5 KSI (thousands of pounds per square inch). Exhaust gas temperatures in opposed-piston engines, as described above, can range from 500 deg. C to 700 deg. C or more. Coating layers (e.g., thermal barrier coatings) applied to the inside surface of a gray iron exhaust plenum chamber can reduce the temperature experienced by the gray iron by at least 100 deg. C. Effectively, the gray iron of an exhaust plenum chamber with a barrier coating can have higher fatigue limit strengths with values between approximately 15 KSI to approximately 23 KSI.

FIG. 6 shows a close-up, cross-sectional view 600 of a coating on an inside surface of the exhaust plenum chamber of FIGS. 4A and 4B. The base metal 610 of the inside surface, for example gray iron, is shown with a coating layer 620 on it with an interface 625 between. The coating layer 620 can have a thickness of between 150 microns and 830 microns, such as between 300 microns and 600 microns. In some implementations, a coating layer on the inner surface of an exhaust plenum chamber can have a thickness between approximately 400 microns and 500 microns.

In general, desirable thermal layer characteristics of the coating layer can include any of low thermal conductivity, thermal fatigue resistance, thermal shock resistance, high-temperature oxidation and corrosion resistance, the ability to radiate heat back to exhaust, and the ability to lower heat rejection outside of the exhaust plenum chamber. The coating layer can include a thermally insulating material, which may be a low heat capacity material. At the interface 625, the base metal 610 can have a surface roughness that allows for good adhesion of the coating layer 620. Thus, the adhesion of the coating layer 620 on the base metal can have a value between 3000 and 5000 PSI (pounds per square inch) when tested using standard mechanical tests.

Materials for the coating layer can include any of a metal, a ceramic, a composite (e.g., cermet), a polymer, a densified material, and a porous material impregnated with polymer or ceramic. Exemplary ceramic materials can include alumina, zirconia, fosterite, mullite, yttria-stabilized zirconia (YSZ). Further, metals used for the coating material can include silicon, nickel, molybdenum, chromium, cobalt, yttrium, aluminum, and alloys thereof. Materials preparation methods for the coating can include any of spray deposition (e.g., plasma spray), electron beam physical vapor deposition (EB-PVD), slurry coating (spray and dip coating), electrolytic processes, and sol-gel processes.

Porosity of the material of the coating layer can be between 10-15 volume %. The coating layer can have a coefficient of thermal expansion (a) between 4 and 17×10⁻⁶ cm/(cm·K), such as between 7.5 and 10.5×10⁻⁶ cm/(cm·K). Another measurable characteristic is the thermal conductivity of a material. The coating layer can have a thermal conductivity value of between approximately 1 and 8 W/(m·K). In some implementations, coating layers can reduce the temperature experienced by the underlying base metal by an amount ranging from about 100 degrees C. to about 350 degrees C.

As described above, particularly with respect to the plot shown in FIG. 10-2 of Boyer, a coating layer (e.g., thermal barrier layer), may reduce the temperature experienced by the base metal of an exhaust plenum chamber during operation of an engine, so that the temperature of the base metal (e.g., gray iron) is below about 450 or 500 degrees C. For gray iron, at temperatures of about 500 degrees C. and below, the fatigue limit is a factor of 2 or 3 of what it is at about 600 degrees C. This means that by maintaining the gray iron of the exhaust plenum chamber below about 500 degrees C., the structural integrity of the chamber can be maintained for a greater amount of time than at the temperature of exhaust gas leaving the engine's cylinders (e.g., about 600 degrees C. or greater).

Similarly, the flow of coolant around and through an exhaust plenum chamber while an engine operates may help maintain the temperature of the base metal below a threshold point (e.g., about 500 degrees C.) to help maintain the fatigue strength and structural robustness of the chamber. In exhaust plenum chamber configurations with both structural posts with passageways for conveying coolant and a thermal barrier coating, there may be even greater likelihood that the temperature of the base metal (e.g., gray iron) is maintained at or below a temperature that allows for optimal fatigue strength, and thus maintenance of the integrity of the exhaust plenum chamber. The inclusion of a thermal barrier coating can reduce heat rejection to coolant and oil by at least approximately 14% when compared to an uncoated exhaust plenum chamber. The inclusion of a thermal barrier coating can also increase the heat to engine exhaust by at least approximately 7% as compared to an uncoated exhaust plenum chamber. The increase in heat in the engine exhaust can increase the exhaust temperature by at least about 9 degrees C., and the increase in heat to engine exhaust can improve brake specific fuel consumption (BSFC). Further, the presence of a thermal barrier coating (e.g., coating layer) in an exhaust plenum chamber of an opposed-piston engine may reduce the cooling needs of the engine. A reduction in cooling needs may allow the cooling system to employ a smaller cooling system, and correspondingly a smaller cooling pump, thus reducing pumping loads.

FIG. 7 shows an exemplary method 700 for making an exhaust plenum chamber of an opposed-piston, uniflow scavenged, two-stroke engine. Initially, the method includes preparing the interior surface of an exhaust plenum chamber of an opposed-piston engine for a coating layer, as in 710. The preparation of the interior surface can include any of cleaning, etching, roughening, smoothing, machining, chemical activation, and the application of a bonding layer. Then, the method includes coating the interior surface of the exhaust plenum chamber with a thermal barrier coating, as in 720. Optionally, the method also includes treating the exhaust plenum chamber after application of the thermal barrier coating so that the opposed-piston engine is prepared for use, as in 730. Treating the exhaust plenum chamber can include a heat treatment, surface finishing, and the like.

Example 1

An opposed-piston engine with an exhaust plenum chamber with a thermal barrier coating was operated for 53 hours, including under high load rated power conditions. The exhaust plenum chamber tested included two posts positioned to receive high velocity blowdown events, and through which coolant flowed at 10 gallons per minute. The back wall of the exhaust plenum chamber was adjacent to the engine gearbox and gearbox oil. The roof and floor of the exhaust plenum chamber communicated to the rest of the engine block. In the tested exhaust plenum chamber, the thickness of the thermal barrier coating varied from 150 microns to 830 microns. The thermal barrier coating used had a specified temperature reduction (i.e. reduction of exhaust plenum chamber wall temperature) of between 100 and 350 degrees C., and had a specific thermal conductivity specified between 0.7 and 2.4 W/m·K.

The heat rejection from this exhaust plenum chamber was compared to a similar engine that included an uncoated exhaust plenum chamber, and the results are shown in FIG. 8. The comparison was made from data taken at matched rated power conditions. By comparing the data from the uncoated exhaust plenum chamber and the coated exhaust plenum chamber, it was calculated that the thermal barrier coating on the coated exhaust plenum chamber reduced heat rejection to coolant and engine oil by approximately 14% and increased heat injection to exhaust by approximately 7%. It was also calculated to be a 9.2 degree C. increase in exhaust temperature.

Though the figures, particularly FIGS. 4A and 4B, show the exhaust plenum chamber as enclosing three cylinders in an in-line configuration, as well as creating an enclosed space with the aid of a cover, other configurations of exhaust plenum chambers are compatible with the coating and coating methods scribed herein. Engines with a single cylinder, two cylinders, or greater than three cylinders can have exhaust plenum chambers with coatings as described above. An exhaust plenum chamber can be formed in a cylinder block (or an engine block) without a large single cover, having instead access ports, multiple smaller covers, or merely the openings for the cylinders and engine conduits and still be compatible with the coatings and methods described.

Those skilled in the art will appreciate that the specific embodiments set forth in this specification are merely illustrative and that various modifications are possible and may be made therein without departing from the scope of the invention which is defined by the following claims. 

What is claimed is:
 1. An opposed-piston engine, comprising: a cylinder block; a cylinder disposed in the cylinder block, the cylinder including a cylinder wall having an interior surface defining a bore centered on a longitudinal axis of the cylinder and intake and exhaust ports formed in the cylinder wall near respective opposite ends of the cylinder, the intake and exhaust ports each including an array of port openings extending through the cylinder wall to the bore; an exhaust plenum chamber in the cylinder block in which the exhaust port of the cylinder is situated such that the exhaust plenum chamber receives all exhaust gas from the cylinder; and a coating on an inside surface of the exhaust plenum chamber that reduces heat transfer from exhaust gas to the cylinder block.
 2. The opposed-piston engine of claim 1, wherein the exhaust plenum chamber comprises at least one support post of the engine block.
 3. The opposed-piston engine of claim 2, wherein the support post comprises a coolant passageway.
 4. The opposed-piston engine of claim 3, wherein liquid coolant flows through the coolant passageway during operation of the engine.
 5. The opposed-piston engine of claim 1, wherein the coating comprises a thermally insulating material.
 6. The opposed-piston engine of claim 5, wherein the thermally insulating material has a low coefficient of thermal conductivity.
 7. The opposed-piston engine of claim 5, wherein the coating comprises any one of zirconia, alumina, a chrome-containing composition, a cobalt-containing composition, a nickel-containing composition, and an yttrium-containing composition, or any combination thereof.
 8. The opposed-piston engine of claim 5, wherein the coating is spray deposited or dip coating deposited onto the inside surface of the exhaust plenum chamber.
 9. The opposed-piston engine of claim 1, wherein the exhaust plenum chamber includes a base metal that comprises gray iron.
 10. The opposed-piston engine of claim 1, further comprising a plurality of cylinders in the cylinder block, the cylinders being disposed in an inline array.
 11. The opposed-piston engine of claim 10, wherein each cylinder comprises a liner retained in a tunnel in the cylinder block.
 12. The opposed-piston engine of claim 1, wherein the cylinder comprises a liner retained in a tunnel in the cylinder block.
 13. The opposed-piston engine any one of claims 1, 10, and 12, wherein the exhaust plenum chamber further comprises at least one exhaust outlet, the at least one exhaust outlet being in fluid communication with one or more of a turbine inlet, an EGR inlet, and an after-treatment device.
 14. The opposed-piston engine of any one of claims 1, 10, and 12 wherein the exhaust plenum chamber comprises at least one engine block support post with a coolant passageway fluidly coupled to a source of liquid coolant.
 15. A method of making an exhaust plenum chamber of an opposed-piston engine, the method comprising applying a coating layer comprising a material of low thermal conductivity to an inside surface of the exhaust plenum chamber, the exhaust plenum chamber comprising at least one post.
 16. The method of claim 15, further comprising preparing a base metal of the inside surface of the exhaust plenum chamber for application of the coating layer.
 17. The method of claim 15 or 16, further comprising treating the exhaust plenum chamber after application of the coating layer.
 18. The method of claim 15, wherein the exhaust plenum chamber further comprises a floor and a ceiling, and wherein the at least one post extends from the floor to the ceiling.
 19. The method of claim 18, wherein the at least one post comprises a conduit or passageway through a center portion of the at least one post, and further wherein the conduit or passageway is fluidly connected to a source of cooling fluid. 